The present invention relates to a semiconductor device and a manufacturing method therefor, and relates more particularly to a semiconductor device that has a thin-film structure with a lamination of polycrystalline layers divided into layers, each having a thickness not larger than a predetermined thickness prescribed according to a fail event, or a semiconductor device that has a thin-film structure with a lamination of polycrystalline layers and layers of another material, of which a main component thereof is different from the main component of the polycrystalline layers, for separating these polycrystalline layers from each other, a method of manufacturing this device, a manufacturing device therefor or, and a method of determining a film thickness of the polycrystalline layers for preventing a fail event of the semiconductor device.
In recent years, amorphous materials have been used widely for various applications, such as for semiconductor device materials and magnetic materials, by taking advantage of such characteristics as isotropy and uniformity that can be obtained from the amorphous materials. As a material for a semiconductor device, amorphous silicon has been widely used for the purpose of easily obtaining a uniform density of an impurity.
When a silicon thin film has been formed as a polycrystalline silicon layer on the surface of a semiconductor substrate, stress generated within the film is sufficiently low so as to be not higher than a few hundred MPa.
After an amorphous film layer has been formed on the surface of the semiconductor substrate, when the amorphous film is exposed to a high temperature higher than the temperature at which a previously-coated amorphous material is crystallized for forming another film made of other material on the film, or for carrying out a heat processing to relax a stress caused by the other layer, or for crystallizing the amorphous material of the film formed, the volume of the film shrinks as the crystallization of the amorphous material progresses, with a result that, in some cases, an extremely large tensile stress reaching 1000 MPa is generated within the film.
Because of failures (such as warp deformation in the wafer, peeling-off between layers, cracks within a layer, etc.) generated within the semiconductor device due to the occurrence of this tensile stress, there has been a case that the reliability of the product was deteriorated seriously. In order to prevent an occurrence of such a defect as described above, a method has been taken that a film having a compressive stress generated within the film or a film having a tensile stress generated within the film is laminated to reduce the total stress, for example as described in the Japanese Patent Unexamined Publication No. JP-A-63-260052.
In relation to the formation of a laminated layer of polycrystalline silicon films in the semiconductor device, there are also other techniques such as described in the Japanese Patent Unexamined Publication No. JP-A-63-29954 and the Japanese Patent Unexamined Publication No. JP-A-3-3326. These techniques provide the techniques for laminating materials of mutually different substances.
However, when an amorphous film is formed on the surface of the semiconductor substrate and the film layer is crystallized to have a polycrystalline layer, the newly grown grain becomes larger as the film thickness is larger and there is a tendency that the proportion of the volume contraction becomes larger As a result, depending on the thickness of the film formed, the tensile stress generated in the amorphous material layer that has been crystallized becomes larger than the bonding strength between the film layers formed or the strength of the materials of the film layers formed, which may result in a failure such as a peeling off between layers or a crack within a layer.
Further, even if the above-described failure has not occurred in the semiconductor device, a film thickness has become a cause for generating a warp deformation in the wafer which may cause a fault at the time of an exposure, or an increase in the dislocation density following an increase in the strain at a film interface of the amorphous material has caused a deterioration in the electric characteristics within the semiconductor device such as an increase in the electric conductivity or an inter-connection. Thus, it has been necessary to provide a limit to a film thickness at the time of forming films in order to control a stress within a film.
In the specification of the present invention, various defects induced by an increase in the stress generated within the semiconductor device will collectively be referred to as xe2x80x9ca fail event of the semiconductor devicexe2x80x9d. An allowable stress level at which none of these fail events will occur may change widely depending on a difference in the process of manufacturing a semiconductor device, a difference in portions of a laminated film which are used for a semiconductor device, physical properties of materials used and a corresponding fail event. Therefore, an allowable stress value at which a fail event of the semiconductor device will not occur will be called a critical stress valuexe2x80x9d.
When a thickness of a polycrystalline phase film which has been obtained by crystallizing an amorphous phase film is small, the crystal grains become fine and a stress generated is lowered and no defect, described in the foregoing will occur. However, the thin film thickness has limited an allowable current that can flow within the film and also has become a cause for a defect such as an electromigration that is generated by an excess current within the film. Thus, it has been difficult to form a film with an optimum film thickness by using a polycrystalline phase film which was produced by crystallizing an amorphous material layer.
Objects of the present invention are as follows.
(1) In a thin-film manufacturing method having a process of depositing amorphous layers and a process of crystallizing the amorphous materials, it is an object of the present invention to provide a method of manufacturing a semiconductor device which can form a film thickness of a required design specification for a thin film structure made of the conductive material that includes an amorphous layer to be crystallized in a later process, and which can eliminate defects, such as a deterioration of electric characteristics of the semiconductor device manufactured, peeling-off between layers, cracks within a layer, etc.
(2) It is an object of the present invention to provide a semiconductor device of a high reliability which can prevent an occurrence of a defect by the method of manufacturing a semiconductor device that is provided in (1).
(3) In a thin-film manufacturing device which can carry out a process of depositing amorphous layers and a process of crystallizing the amorphous materials, it is an object of the present invention to provide a device for manufacturing a thin film which can automatically control the process of forming an amorphous layer and the process of crystallizing the amorphous material, in an integrated process without exposing the thin film in manufacturing to the atmosphere.
(4) In order to achieve the objects (1) to (3) of the present invention, it is an object of the present invention to provide a method of determining a maximum value of a film thickness in which an amorphous layer can be deposited at one time to ensure that an occurrence of a fail event is prevented, not based on experience.
In order to achieve the above-described objects, the present invention has the following characteristics.
A semiconductor device of the present invention has conductive thin films and is characterized by the following. (1) At least a part of the thin-film has a laminated structure divided along a film thickness direction, and each of the divided layers has a main component made of the same element or the same compound. (It is desirable that the main component is a material including silicon atom or metal silicide. The material of each layer may be different from that of the other by doping). (2) At least a part of the thin-film has a laminated structure divided along a film thickness direction, and an average crystal grain size of the grains within each one of the divided layers is about xc2xd times to about ten times of the thickness of the divided layer. (For example, the grain size is equal to the thickness of the divided film or is in the same order or is about a fraction or several times as the divided film thickness.) (3) Additionally, or alternately, at least a part of the thin-film has a laminated structure divided along a film thickness direction, and the thickness of each layer is not larger than a thickness prescribed by a critical stress value that is determined according to a fail event of the semiconductor device.
In either case, a semiconductor device is the one having a thin-film structure made of the same conductive material and it is desirable that the thin film is divided, at least once, along its film thickness direction. It is also desirable that the thin film consists of at least two polycrystalline layers and the thin film is applied to a portion selected from a group of electrodes (preferably a gate electrode) and wiring layers. It is also effective to have another layer made of a material different from that of the polycrystalline layer, at a position for separating the polycrystalline layer into layers. It is also effective to have different densities of impurity in adjacent layers of at least one pair of adjacent layers of the thin film divided along the film thickness direction.
The semiconductor device of the present invention is also characterized in that a trench or a rugged surface is provided on the surface of the semiconductor substrate, that a conductive multi-layer thin film is formed on a part or a whole of the trench or the rugged surface of the surface of the semiconductor substrate so as to cover a portion of a corner formed by at least the semiconductor substrate surface, the trench and the rugged surface, and that each layer has a main component which is the same element or the same compound. In this case, it is desirable that the conductive multilayer thin film is polycrystalline and the thickness of each layer structuring the thin film is not larger than the thickness prescribed by a critical stress level to be determined according to a fail event of the semiconductor device. It is also effective to have a layer made of a material different from that of the polycrystalline layers, at a position for separating adjacent ones of the polycrystalline layers. It is also effective to have different densities of impurity at least between a pair of adjacent layers of the thin film divided in the film thickness direction.
The semiconductor device of the present invention is also characterized in that it has a laminated layer structure of a metal silicide thin film divided along a film thickness direction by at least one time.
Implementation status of the semiconductor device according to the present invention is as follows. (1) The semiconductor has a polycrystalline layer obtained from the process of depositing an amorphous layer and a process of crystallizing the amorphous material and there are at least two continuous deposited layers of polycrystalline material whose main component is made of the same material. (2) Each of the laminated polycrystalline layers has a thickness not larger than a thickness prescribed by a critical stress level determined according to a fail event of the semiconductor device. (3) In a semiconductor device having a gate electrode, there are at least two continuous deposited layers of polycrystalline material whose main component is the same material in the whole or part of the gate electrode structure on the semiconductor substrate.
The method of manufacturing a semiconductor device according to the present invention includes a process of depositing layers of amorphous materials on the semiconductor substrate and a process of crystallizing the deposited amorphous materials, and is characterized in that either (1) the process of depositing layers of amorphous materials is divided into a plurality of times and the crystallization is carried out for each process of depositing each amorphous layer, or (2) the process of depositing amorphous layers is divided into a plurality of times, a material whose main component is different from that of the amorphous material, is deposited to separate an amorphous layer from an adjacent amorphous layer at each process of depositing each amorphous layer and the amorphous material is crystallized at least after finishing all the deposition processes. In the case of (2), it is desirable that the amorphous material is silicon and the main component for separating the amorphous layers which is different from the amorphous material is a metal which generates a silicide reaction.
In either case, it is desirable that the method of manufacturing a semiconductor device according to the present invention includes the process of differentiating, between at least a pair of adjacent layers, the density of impurity therein, or includes the process of crystallizing the amorphous material which is the crystallization process of an amorphous material by a laser irradiation on either the whole surface of the amorphous layer or on only a selective local portion of the amorphous layer.
The deposition method of thin films according to the present invention includes a process of depositing layers of amorphous materials and a process of crystallizing the amorphous materials, and is characterized in one of the following: (1) the process of depositing layers of amorphous materials is divided into a plurality of times and the crystallization process is applied to each amorphous layer, (2) densities of impurity within the plurality of layers of amorphous materials are different between at least an adjacent pair of layers, (3) the process of depositing amorphous layers is divided into a plurality of times, a material whose main component is different from that of the amorphous material is deposited to separate an amorphous layer from an adjacent amorphous layer and the amorphous layers are crystallized at least after finishing all the processes, and (4) the process of crystallizing the amorphous material which is the crystallization process of an amorphous material by a laser irradiation on either the whole surface of the amorphous layer or on only a selective local portion of the amorphous layer.
The method of manufacturing a thin film according to the present invention is a method of obtaining a metal silicide thin film by generating a silicide reaction by laminating a silicon thin film with a metal thin film, and is characterized in that a metal thin film and a silicon thin film are laminated at least two times respectively and that the film thickness of each laminated layer is not thicker than a film thickness prescribed by a fail event and the metal silicide thin film is manufactured by generating a silicide reaction.
In either case, it is desirable that the method of manufacturing a thin film according to the present invention provides a film thickness of each amorphous layer deposited at one time to be not larger than a film thickness prescribed by a critical stress value that is determined according to a fail event.
The device for manufacturing a semiconductor device according to the present invention is a device for carrying out a process of depositing layers of amorphous materials and a process of crystallizing the amorphous material and is characterized in that the manufacturing device has a chamber for installing a semiconductor substrate in it, a tool for supporting the semiconductor substrate, a heating unit for adjusting a temperature inside the chamber and a temperature of the substrate, units for adjusting volumes of gases to be taken in corresponding to the number and kinds of gas to be flown into the chamber, a unit for adjusting a pressure of gas inside the chamber, an exhaust unit for exhausting air from the chamber, and a unit for automatically controlling said chamber, said heating unit, said flow rate adjusting unit, said gas pressure adjusting unit and said exhausting unit, and the control unit controls a process of continuously or intermittently depositing amorphous thin films a plurality of times and a process of crystallizing these thin films, to form a laminated thin film structure on the semiconductor substrate. It is desirable that this device has at least one laser irradiating unit and a unit for automatically controlling this laser irradiating unit to carry out an automatic control and an automatic processing in the processes of manufacturing a semiconductor device.
The method of determining a film thickness according to the present invention is a method of determining a film thickness of deposited thin films for carrying out a process of depositing layers of amorphous materials and a process of crystallizing the amorphous material, and is characterized in that a film thickness of an amorphous layer to be deposited at one time is determined to be a level not higher than a critical stress value to be determined according to a fail event, based on a relationship between a film thickness of an amorphous layer and an average size of a crystal grain generated in a polycrystalline layer obtained by crystallizing the amorphous material and a relationship between a film thickness of a polycrystalline layer obtained by crystallizing the amorphous material and a stress generated.
Terms to be used in the specification of the present invention will be explained as follows.
Main component: This refers to a portion excluding three types of impurities; an impurity for positively carrying out doping, an impurity originally included in a raw material such as a gas or a target, and an impurity which is unavoidably mixed into a semiconductor during a manufacturing process.
Conductivity (of a thin film): This refers to a conductivity of a metal or semiconductor. In other words, volume resistivity of a semiconductor is between a metal and an insulator and is about 10xe2x88x925 to 108 xcexa9xc2x7m. The volume resistivity is lower as the impurity density is higher, and this shows a value near 0 at an absolute zero degree. Accordingly, when volume resistivity of a thin film is not higher than 108 xcexa9xc2x7m, the thin film is said to have a conductivity according to the present invention.
Average grain size of crystal (in a deposited film surface): A density of an occurrence of a crystal nucleus differs depending on an impurity density of a deposited film and a heating condition, and this becomes xc2xd times to 10 times depending on a condition for an occurrence of a crystallization. In the present invention, a crystallization (reaction) of a grain size of about xc2xd times to 10 times of a film thickness of each divided layer is desirable.
A layer generated by a silicide reaction: A layer may be amorphous or polycrystalline at time of deposition and a film to be formed in the end should be polycrystalline.
A fail event of a semiconductor device: A collective name of various failures caused by an increase in the stress generated within a semiconductor device, such as a peeling-off between layers, a crack within a layer, or a crystalline defect.
Allowable stress level: An allowable stress value at which a fail event of a semiconductor will not occur. A permissible stress level at which a fail event will not occur varies depending on a difference in a process of manufacturing a semiconductor device, a difference in a portion at which a laminated film is used for a semiconductor device, physical characteristics of a material a corresponding fail event, etc.
Trench capacitor: a capacitor to be used for a memory cell of a DRAM (Dynamic Random Access Memory) whose memory capacity exceeds 1 M bits. When a capacitor is provided in a side wall of a deep trench formed by etching a silicon substrate to increase capacitance, a large capacitance can be obtained even if a capacitor area becomes finer further.
LOCOS: A silicon oxide film for electrically separating among devices.
Primary recrystallization: If a range in which an atom is arrayed orderly is considered to be a crystal, it can be considered from a micro viewpoint that a crystal also exists within a substance of an amorphous state. However, primary recrystallization in the present invention refers to a phase change of an amorphous substance into a crystal, that is, a crystallization (reaction). Generally, a primary recrystallization refers to a fining of crystal grains when a material which has been cold worked and composed of many crystal defects has been heated. However, in the present invention, this term is used to emphasize that an average size of a grain is approximately a size obtained by a primary recrystallization, which is discriminated from a secondary recrystallization where a fine crystal grows large at a temperature an atom is activated.
It has been generally known that when the process of crystallizing an amorphous material is carried out at a temperature at which a primary recrystallization reaction is generated after the process of depositing films of amorphous layers, the size of a crystal grain of a film obtained by crystallizing the amorphous material becomes an order of a film thickness and a film with almost no existence of a grain boundary in the film thickness direction is formed.
The grain boundary is an incommensurate portion between crystal grains at which atomic array directions do not agree with each other and, therefore, a region where many local defects (such as a dislocation, a lattice vacancy, and a cavity) exist.
In crystallizing an amorphous material by heat processing, when a film thickness is large, the crystal grain size becomes large and the ratio of a grain boundary which holds a higher defect density in the total film region is small, so that the ratio of a volume contraction of the film becomes large and a tensile stress within the film becomes large. On the other hand, when the film thickness is small, the crystal grain size becomes small, and a ratio of a grain boundary in the total film region becomes relatively large. Therefore, the ratio of a volume contraction becomes relatively small and a tensile stress can be minimized.
The crystal grain size referred to in this specification means an average value of a distance between adjacent grain boundaries in a direction on parallel to the film surface in a desired cross section of a polycrystalline thin film in which a crystallization reaction has been completed.
FIG. 15 shows an example of a measurement of a stress (crystallization stress) generated as a result of a crystallization reaction carried out within an amorphous silicon film by changing a film thickness. In FIG. 15, the horizontal axis shows a total thickness of films deposited and the vertical axis shows a stress generated inside the films as a result of a crystallization reaction when the total films deposited have been crystallized at one time. As shown by this drawing, it is clear that when the thickness of films deposited increases the stress generated at the time of the crystallization reaction increases.
Accordingly, it is effective to control the film thickness so that the stress generated by the crystallization reaction is set to be not higher than a critical stress level prescribed by each fail event, to prevent an occurrence of a peeling between thin films, cracks within thin films or a dislocation inside the semiconductor substrate.
According to the present invention, in the process of manufacturing a semiconductor device including the process of depositing amorphous layers, the thickness of amorphous layers deposited at one time is limited to be not higher than a thickness prescribed by a critical stress level determined according to a fail event and the amorphous material is crystallized, so that the size of a crystal formed within a polycrystalline layer obtained by the primary recrystallization of the amorphous layers is limited to be on the order of a thickness of films of the amorphous layers deposited.
As a result, the size of the crystal grains formed within a polycrystalline layer is limited and the stress generated within the polycrystalline layer can be reduced to be not higher than the critical stress level at which a fail event is not generated.
By laminating the polycrystalline layers whose stress has been reduced, the film thickness of the thin film structure can be set to the thickness necessary for the specification of a design, and it is possible to prevent an occurrence of a deterioration of electric characteristics of a semiconductor device to be manufactured and defects such as peeling-off between layers and cracks within a layer induced by a stress. Thus, it is possible to obtain a high reliability of a semiconductor device to be manufactured and a high production yield of the product.
Further, in the thin film manufacturing device which can carry out the process of depositing amorphous layers and the process of crystallizing the amorphous material, it is possible to carry out the process of depositing films of amorphous layers and the process of crystallizing the amorphous material by an automatic control in an integrated process without exposing the thin films during a manufacturing process into the atmosphere.